SERVICE MANUAL FOR M28 ONE-CHIP CHASSIS

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1 TCL OVERSEAS HOLDINGS LIMITED Service Manual 3 SERVICE MANUAL FOR M28 ONE-CHIP CHASSIS PART I. Servicing Precautions When working, the unit is with high voltage about 25KV inside. So, to avoid the risk of electric shock, be careful to adjust the chassis! 1. Only qualified personnel should perform service procedures. 2. All specification must be met over line voltage ranger of 110V AC to 240V AC 50Hz/60Hz. 3. Do not operate in WET/DAMP conditions. 4. Portions of the power supply board are hot ground. The remaining boards are cold ground. 5. Discharge of CRT anode should be done only to CRT ground strap. 6. When fuse blow, ensure to replace a fuse with the same type and specification. 7. Keep the wires away from the components with high temperature or high voltage. 8. When replacing the resister with high power, keep it over the PCB about 10mm. 9. The CRT anode high voltage has been adjusted and set in the factory. When repairing the chassis, do not make the high voltage exceed 27.5KV (The beam current is 0uA). Generally, the high voltage is set on 25.5KV±1.5KV (The beam current is 700uA). * The values of parameters above are for information only. 10. Before return the fixed unit, do check all the covering of wires to ensure that not fold or not short with any metal components. Check the entire protection units, such as control knobs, rear cabinet & front panel, insulation resister & capacitor, mechanical insulators and so on. 11. There are some mechanical and electrical parts associating with safety (EMC) features (Generally related to high voltage or high temperature or electric shock), these features cannot be found out from the outside. When replace these components, perhaps the voltage and power suit the requirements, but efficient X-ray protection may not be provided. All these components are marked with in the schematic diagram. When replace these, you d better look up the components listed in this manual. If the component you replaced not has the same safety (EMC) performance, harmful X-ray may be produced.

2 4 Service Manual TCL OVERSEAS HOLDINGS LIMITED PART II -Product Specification 1. Ambient Conditions: 1.1 Ambient Temperatures: a. Operating: -10 ~ +40 b. Storage: -15 ~ Humidity a. Operation: <80% b. Storage: <90% 1.3 Air Pressure: 86kpa ~ 106kpa 2. GENERAL SPECIFICATION 2.1 MPU & Chroma IC: TMPA8803CSN (One-Chip) 2.2 TV Broadcasting System PAL DK/BG SECAM DK/BG NTSC 3.579/4.43 AV MODE 2.3 Scanning Lines & Frequencies 525/625 lines KHz/15.75KHz 50/60Hz 2.4 Color Sub-Carrier: 4.433MHz/3.579MHz 2.5 IF: Picture 38.9MHz Sound 5.5/6.5MHz 2.6 Power Consumption: 80W 2.7 Power Supply: AC 220V 50Hz±10% 2.8 Audio Output Power (7%THD): 4W + 4W 2.9 Aerial Input Impedance: 75 Unbalanced Din Jack Ant.Input 2.10 Product Safety Requirement: VDE Approval 2.11 Product EMC/EMI Requirement: FTZ Approval 3. Basic Features of Controller 3.1 Channel Tuning Method: Voltage Synthesizer

3 TCL OVERSEAS HOLDINGS LIMITED Service Manual Presettable Program: 100 Programs 3.3 Tuning for VHF and UHF Bands: Auto/Manual/Fine Tuning 3.4 Picture and Sound Adjustment Bright, Contrast, Color and Volume Control TINT Control (NTSC) Sharpness Control 3.5 OSD General Features (Volume, Brightness, Contrast, Color, Program, Band, Auto Search, Manual, Tune, Muting, AV and Sleep Timer) NICAM and Dual Language German Stereo Indicator 3.6 Sleep Timer: Minutes with 10Min.Increment 3.7 Auto Off When No Broadcasting Signal: 15 min 3.8 Full Function Infrared Remote Control 3.9 Remote Effective Distance: 8m 4. Construction of Front Panel Main Power Switch Remote Sensor Standby Indicator Menu Select TV/AV Select Program and Volume Up/Down 5. Construction of Real Panel 75 Aerial Terminal RCA Socket Audio-R+L In/Out, Video- In/Out Y/U/V Input 6. Other Information 6.1 Colour Temperature: 9300K X=284 Y= Magnetic Field: Bv=0.2~0.5Gs

4 6 Service Manual TCL OVERSEAS HOLDINGS LIMITED PART III. Brief Introduction on Chassis AV INPUT/ OUTPUT RF IN TUNER SAW NICAM BD AUDIO AMP XTAL OSC TMPA8803CPN(M28) R/G/B CRT DRIVE I 2 C BUS E 2 PROM INFRARED REMOTE CONTROL REMOTE CONTROL RECEIVER V OUTPUT DPC H DRIVE H OUTPUT FBT SWITCH POWER MC44608 The TV signal is amplified by the frequency mixing circuit of the tuner. Then the tuner output PIF and SIF signals. The IF signals are amplified about 20dB by the pre IF amplifier (Q101). Having passed the SAW, the IF signals go into the TMP8803CPN from pin 42, 41. The IF signal pass the video detect circuit to generate CVBS signal. Then the processor deals the signal with luminance and chroma separation. The processor deals the luminance signal with Y-Delay, Y-Gamma correction, Y-hf compensation and black strength, all which ensure that there are enough bandwidth and gain with Y signal, so that the resolution of picture detail is improved and the Y signal is well timed with chroma signal. The processor also deals the chroma signal with chroma sub-carrier recovery, color system recognition and color signal decoding, then outputs B-Y and R-Y color difference signal. A matrix circuit converts the color difference signal (Y, B-Y and R-Y) into primary color signal (R/G/B). On the other hand, the processor separated the horizontal and vertical sync signal from the CVBS signal which was generated by video detect circuit. Having passed the horizontal (or vertical) frequency dividing circuit, the H (or V) OSC signal, which be generated by H-AFC (or V-AFC), is changed to H (or V) drive signal. The H/V drive signal make the horizontal/vertical circuits and scan output circuit to generate H/V saw tooth wave

5 TCL OVERSEAS HOLDINGS LIMITED Service Manual 7 1.Channel Section The RF signal is converted into IF signal by the tuner. Then the IF signal cross the IF amplifier circuit (pre IF amplifier) to get a gain about 15dB. By the coupling capacitance (c110) and the match resistance (R ), the input resistance of the pre-if amplifier match with the tuner. The signals pass a parallel connection circuit with voltage NFB, which combines the advantages of low output impedance, of wide dynamic range and of less components. R116 is a voltage NFB component, which is used to adjust the gain in the pass band. Having been amplified by the IF amplifier, the IF signal pass a SAW, and then come into TMPA8803CSN from pin41 and pin42 with balance. The processor deal the IF signal with IF detection, PLL demodulation, IF AGC, AFC, video peak detection, and color system recognition etc., then output a AGC signal from pin 43 to the tuner to adjust the input amplitude of IF signal. R217, C218 and C219 make up of picture IF PLL circuit, which is used to control IF detection. IC201 output a sound IF signal from pin 31 and a video signal, which will be amplified by Q209, from pin30. The processor output a sound system control signal to Q208. If the processor output a high level from pin59 (sound detection), Q208 is on, and a video signal is separated from the IF signal by a trap. With capacitance coupling, the video signal comes into IC201 from pin26, and then it is selected by inner switches and output from pin45. Having come out, the video signal will be amplified by Q210, and a sync signal will be separated by a sync separate circuit which is made up by C208, Q202 and Q203. Then the video come into inner 870X CPU module from IC201 pin62 to detect whether the signal is live signal. Tuning control and band switch control circuits The processor output a tuning control signal from pin60. The control signal will pass Q103 common emitter amplifying circuit, then an integrating circuit. Finally, it is added to the VT terminal to provide all channels tuning voltage for the tuner to stabilize the channels. 2.Vertical Output Section TMPA8803CSN outputs vertical saw-tooth wave from pin 16. It come to pin5 of LA7840 with DC coupling, and is amplified by inner difference amplifier. Pin4 of LA7840 is the same phase input terminal. R307 and R308 are DC offset resistances. C305 is a filter capacitor. In application to M28, pin4 of la7840 is fixed as the DC amplify ref terminal. The amplified saw tooth wave come out la7840 from pin2 and make the deflect coil to generate the deflect current. R314 and C301 filtrate the inductive interference from the horizontal deflect coil. R317 and C309 are used to eliminate spurious oscillation generated by the deflect coil and distributed capacitance resonance. C308, R313, C307 and accessory circuit are in charge of draw AC saw tooth wave out at the deflect coil terminal connected with R315 & R316, and feedback to the input terminal of la7840 (pin5) to correct the linearity of horizontal scan. C306 is a high frequency decoupling capacitor. D301 and C303 make up of a voltage pump up circuit. La7840 output a vertical kickback impulse from pin7 to locate the OSD characters. 3.Horizontal Output Section The processor outputs horizontal drive impulse from pin 13. The drive impulse is done with voltage division by R238 and R401, and then comes to the base of the drive triode (Q401). C401 is used to eliminate the noise in the H drive impulse. T401 is a horizontal drive transformer. Q402 is a horizontal output triode with a damper inside. L402 is connected with the emitter of the horizontal output diode to eliminate the radiation and to improve the distortions at the cross of vertical and horizontal white

6 8 Service Manual TCL OVERSEAS HOLDINGS LIMITED lines. C406 and C402 are retrace capacitors and C421 is an s-correct capacitor. L441 and L442 are horizontal linear inductors. R441 is used to eliminate the parasitic oscillation caused by horizontal linear inductors. C420, R413 and D411 are used to correct the M-distortion in horizontal direction. C422, R415 and R415A are coupling components for the horizontal retrace impulse, which are feed back to pin 12 of TMPA8803CSN. D404 is a negative peak-killer diode. Horizontal scanning distortion and the method to compensate it The deflect coil and the horizontal output triode have some resistance R while they are ducting. The resistance R will cause the non-linear distortion, which means that the right direction scanning speed of the electron beam becomes slower, and the right of the raster is compressed to generate distortion. We use a horizontal linear adjuster to compensate this kind of distortion. We use L412 and L411 as the H linear adjusters in H scanning section of M28 chassis. R411, which is parallel connected with L411 and L412, is a despiking resistance for preventing the oscillation by compensating inductor and the stray capacitance. The linear adjuster is a transductor coil with a magnetic core inside. If the current, which pass the linear adjuster coil, increase to a certain value, the magnetic core becomes saturated to decrease the inductance of the linear adjustment inductor. If the +B is steady, the increase speed of Iy is faster to compensate the reducing of deflecting current by the resistance R mention above. We can adjust the magnetic core to chang the inductance of the linear compensate inductor to adjust the H linearity. The EHT generation circuit The FBT supply the anode high voltage, focus voltage and screen voltage for M28 chassis. D401 and C408 are in charge of regulating the primary impulse of the transformer to output a voltage of 190V for the video amplifiers. The ( 10 ) ~ ( 8 ) coils of the FBT supply the heater with power. Having passed the divider and clipping circuits, which are maded up by R415, R415A, C422 and D404, the H retrace impulses getting out from ( 3 ) ~ ( 10 ) coils are inputed to pin12 of TMPA8803CSN to generate sand castle impulse. To limit the beam current in a safe range, we add a ABL circuit in M28 chassis. We add two sampling resistances (R414, R415) between +24V power supply and pin7 of the FBT. The voltage at the joint of the two resistances is feed back to pin27 of TMPA8803CSN to control bright and contrast to limit the beam current. It is also in charge of regulating EHT. C410 is a fliter capacitor for ABL voltage. The impulses, which are induced by secondary coil 5, are changed to 12V once passed the regulating and fliting circuit made up by D402 and C413. IC401 change 12V power supply to 9V for many circuits, such as R/G/B output circuit of TMPA8803CSN, IC4053, pre IF-amplifier circuit, bright dots killer circuit and S terminal circuit. IC402 outputs a 5V power supply for the keyboard circuit. C418, C417, C423 and C425 are fliter capacitors. D402 and C413 are incharge of regulating and flitering for the output of coil6 to supply the V scanning output section with 24V power. The 24V is added to the upper terminal of the V deflecting yoke as the DC bias for the movement of V center. Extension distortion and compensation This kind of distortion is mainly caused by the structure of CRT. Due to the srcreen of SF CRT is not a ture flat screen, the distances from the deflecting center to the screen are not the same. The scanning speed of the electron beam is uniform. If the electron beam scannning the screen equally with the

7 TCL OVERSEAS HOLDINGS LIMITED Service Manual 9 effect of ture linear sawtooth current, the E-W sides of the picture are stretched. That is the extension distortion. Usually, we add a S-correct capacitor in series with the deflecting coil to compensate this kind of distortion. The integral character of S-correct capacitor make the current waveform S shape. So the scanning speed of electron beam at the center of screen is faster than the one at the side. So this action can correct the extension distortion. C421 is a S-correct capacitor. The capacitance is inverse ratio with the correcting effect.

8 10 Service Manual TCL OVERSEAS HOLDINGS LIMITED PART IV. IC Pin Description 1. MC44608-High Voltage PWM Controller Pin Name Description 1 Demag The Demag pin offers 3 different functions: Zero voltage crossing detection (50mV), 24 A current detection and 120 A current detection. The 24 A level is used to detect the secondary reconfiguration status and the 120 A level to detect an Over Voltage status called Quick OVP. The Current Sense pin senses the voltage developed on the series resistor inserted in the source of the power MOSFET. When Isense reaches 1V, the Driver output (pin 5) is disabled. This is known as the Over Current Protection 2 3 I sense Control Input function. A 200 A current source is flowing out of the pin 3 during the start up phase and during the switching phase in case of the Pulsed Mode of operation. A resistor can be inserted between the sense resistor and the pin 3, thus a programmable peak current detection can be performed during the SMPS stand by mode. A feedback current from the secondary side of the SMPS via the opto coupler is injected into this pin. A resistor can be connected between this pin and GND to allow the programming of the Burst duty cycle during the Stand by mode. 4 Ground This pin is the ground of the primary side of the SMPS. 5 Driver The current and slew rate capability of this pin are suited to drive Power MOSFETs. This pin is the positive supply of the IC. The driver output gets disabled when 6 V CC the voltage becomes higher than 15V and the operating range is between 6.6V and 13V. An intermediate voltage level of 10V creates a disabling condition called Latched Off phase. 7 This pin is to provide isolation between the Vi pin 8 and the VCC pin 6. 8 V i This pin can be directly connected to a 500V voltage source for start up function of the IC. During the Start up phase a 9 ma current source is internally delivered to the VCC pin 6 allowing a rapid charge of the VCC capacitor. As soon as the IC starts up, this current source is disabled.

9 TCL OVERSEAS HOLDINGS LIMITED Service Manual 11 OPERATING DESCRIPTION Regulation The pin 3 senses the feedback current provided by the opto-coupler. During the switching phase the switch S2 is closed and the shunt regulator is accessible by the pin 3. The shunt regulator voltage is typically 5V. The dynamic resistance of the shunt regulator represented by the zener diode is 20. The gain of the Control input is given on Figure 10 which shows the duty cycle as a function of the current injected into the pin 3. A 4KHz filter network is inserted between the shunt regulator and the PWM comparator to cancel the high frequency residual noise. The switch S3 is closed in Stand by mode during the Latched Off Phase while the switch S2 remains open. (See section PULSED MODE DUTY CYCLE CONTROL). The resistor Rdpulsed (Rduty cycle burst) has no effect on the regulation process. This resistor is used to determine the burst duty cycle described in the chapter Pulsed Duty Cycle Control on page 8. PWM Latch The MC44608 works in voltage mode. The on time is controlled by the PWM comparator that compares the oscillator sawtooth with the regulation block output. The PWM latch is initialized by the oscillator and is reset by the PWM comparator or by the current sense comparator in case of an over current. This configuration ensures that only a single pulse appears at the circuit output during an oscillator cycle. Current Sense The inductor current is converted to a positive voltage by inserting a ground reference sense resistor R Sense in series with the power switch. The maximum current sense threshold is fixed at 1V. The peak current is given by the following

10 12 Service Manual TCL OVERSEAS HOLDINGS LIMITED equation: Ipk max = 1/R sense ( ) (A) In stand by mode, this current can be lowered as due to the activation of a 200 A current source: Ipk MAX-STBY The current sense input consists of a filter (6k, 4pF) and of a leading edge blanking. Thanks to that, this pin is not sensitive to the power switch turn on noise and spikes and practically in most applications, no filtering network is required to sense the current. Finally, this pin is used: as a protection against over currents (I sense > I) as a reduction of the peak current during a Pulsed Mode switching phase. The overcurrent propagation delay is reduced by producing a sharp output turn off (high slew rate). This results in an abrupt output turn off in the event of an over current and in the majority of the pulsed mode switching sequence. Demagnetization Section The MC44608 demagnetization detection consists of a comparator designed to compare the V CC winding voltage to a reference that is typically equal to 50mV. This reference is chosen low to increase effectiveness of the demagnetization detection even during start up. A latch is incorporated to turn the demagnetization block output into a low level as soon as a voltage less than 50 mv is detected, and to keep it in this state until a new pulse is generated on the output. This avoids any ringing on the input signal which may alter the demagnetization detection. For a higher safety, the demagnetization block output is also directly connected to the

11 TCL OVERSEAS HOLDINGS LIMITED Service Manual 13 output, which is disabled during the demagnetization phase. The demagnetization pin is also used for the quick, programmable OVP. In fact, the demagnetization input current is sensed so that the circuit output is latched off when this current is detected as higher than 120 A. This function can be inhibited by grounding it but in this case, the quick and programmable OVP is also disabled. Oscillator The MC44608 contains a fixed frequency oscillator. It is built around a fixed value capacitor CT succesively charged and discharged by two distinct current sources ICH and IDCH. The window comparator senses the CT voltage value and activates the sources when the voltage is reaching the 2.4V/4V levels. The complete demagnetization status DMG is used to inhibit the recharge of the CT capacitor. Thus in case of incomplete transformer demagnetization the next switching cycle is postpone until the DMG signal appears. The oscillator remains at 2.4V corresponding to the sawtooth valley voltage. In this way the SMPS is working in the so called SOPS mode (Self Oscillating Power Supply). In that case the effective switching frequency is variable and no longer depends on the oscillator timing but on the external working conditions (Refer to DMG signal in the Figure 5). The OSC and Clock signals are provided according to the Figure 5. The Clock signals correspond to the CT capacitor discharge. The bottom curve represents the current flowing in the sense resistor Rcs. It starts from zero and stops when the sawtooth value is equal to the control voltage Vcont. In this way the SMPS is regulated with a voltage mode control. Overvoltage Protection The MC44608 offers two OVP functions: a fixed function that detects when V CC is higher than 15.4V a programmable function that uses the demag pin. The current flowing into the demag pin is mirrored and compared to the reference current Iovp (120 A). Thus this OVP is quicker as it is not impacted by the V CC inertia and is called QOVP. In both cases, once an OVP condition is detected, the output is latched off until a new circuit

12 14 Service Manual TCL OVERSEAS HOLDINGS LIMITED START UP. Start up Management The Vi pin 8 is directly connected to the HV DC rail Vin. This high voltage current source is internally connected to the V CC pin and thus is used to charge the V CC capacitor. The VCC capacitor charge period corresponds to the Start up phase. When the V CC voltage reaches 13V, the high voltage 9mA current source is disabled and the device starts working. The device enters into the switching phase. It is to be noticed that the maximum rating of the Vi pin 8 is 700V. ESD protection circuitry is not currently added to this pin due to size limitations and technology constraints. Protection is limited by the drain substrate junction in avalanche breakdown. To help increase the application safety against high voltage spike on that pin it is possible to insert a small wattage 1k series resistor between the Vin rail and pin 8. The Figure 6 shows the V CC voltage evolution in case of no external current source providing current into the V CC pin during the switching phase. This case can be encountered in SMPS when the self supply through an auxiliary winding is not present (strong overload on the SMPS output for example). The Figure 16 also depicts this working configuration. In case of the hiccup mode, the duty cycle of the switching phase is in the range of 10%. Mode Transition was observed The LW latch Figure 7 is the memory of the working status at the end of every switching sequence. Two different cases must be considered for the logic at the termination of the SWITCHING PHASE: 1. No Over Current

13 TCL OVERSEAS HOLDINGS LIMITED Service Manual An Over Current was observed These 2 cases are corresponding to the signal labeled NOC in case of No Over Current and OC in case of Over Current. So the effective working status at the end of the ON time memorized in LW corresponds to Q=1 for no over current and Q=0 for over current. This sequence is repeated during the Switching phase. Several events can occur: 1. SMPS switch OFF 2. SMPS output overload 3. Transition from Normal to Pulsed Mode 4. Transition from Pulsed Mode to Normal Mode 1. SMPS SWITCH OFF When the mains is switched OFF, so long as the bulk electrolithic bulk capacitor provides energy to the SMPS, the controller remains in the switching phase. Then the peak current reaches its maximum peak value, the switching frequency decreases and all the secondary voltages are reduced. The V CC voltage is also reduced. When V CC is equal to 10V, the SMPS stops working. 2. Overload In the hiccup mode the 3 distinct phases are described as follows (refer to Figure 6): The SWITCHING PHASE: The SMPS output is low and the regulation block reacts by increasing the ON time (dmax = 80%). The OC is reached at the end of every switching cycle. The LW latch (Figure 7) is reset before the VPWM signal appears. The SMPS output voltage is low. The V CC voltage cannot be maintained at a normal level as the auxiliary winding provides a voltage which is also reduced in a ratio similar to the one on the output (i.e. Vout nominal / Vout short circuit). Consequently the V CC voltage is reduced at an operating rate given by the combination V CC capacitor value together with the I CC working consumption (3.2mA) according to the equation 2. When V CC crosses 10V the WORKING PHASE gets terminated. The LW latch remains in the reset status. The LATCHED OFF PHASE: The V CC capacitor voltage continues to drop. When it reaches 6.5V this phase is terminated. Its duration is governed by equation 3. The START UP PHASE is reinitiated. The high voltage start up current source ( I CC1 = 9mA) is activated and the MODE latch is reset. The V CC voltage ramps up according to the equation 1. When it reaches 13V, the IC enters into the SWITCHING PHASE. The NEXT SWITCHING PHASE: The high voltage current source is inhibited, the MODE latch (Q=0) activates the NORMAL mode of operation. Figure 2 shows that no current is injected out pin 2. The over current sense level corresponds to 1V. As long as the overload is present, this sequence repeats. The SWITCHING PHASE duty cycle is in the range of 10%.

14 16 Service Manual TCL OVERSEAS HOLDINGS LIMITED 3. Transition from Normal to Pulsed Mode In this sequence the secondary side is reconfigured (refer to the typical application schematic on page 13). The high voltage output value becomes lower than the NORMAL mode regulated value. The TL431 shunt regulator is fully OFF. In the SMPS stand by mode all the SMPS outputs are lowered except for the low voltage output that supply the wake up circuit located at the isolated side of the power supply. In that mode the secondary regulation is performed by the zener diode connected in parallel to the TL431. The secondary reconfiguration status can be detected on the SMPS primary side by measuring the voltage level present on the auxiliary winding Laux. (Refer to the Demagnetization Section). In the reconfigured status, the Laux voltage is also reduced. The V CC self powering is no longer possible thus the SMPS enters in a hiccup mode similar to the one described under the Overload condition. In the SMPS stand by mode the 3 distinct phases are: The SWITCHING PHASE: Similar to the Overload mode. The current sense clamping level is reduced according to the equation of the current sense section, page 5. The C.S. clamping level depends on the power to be delivered to the load during the SMPS stand by mode. Every switching sequence ON/OFF is terminated by an OC as long as the secondary Zener diode voltage has not been reached. When the Zener voltage is reached the ON cycle is terminated by a true PWM action. The proper SWITCHING PHASE termination must correspond to a NOC condition. The LW latch stores this NOC status. The LATCHED OFF PHASE: The MODE latch is set. The START UP PHASE is similar to the Overload Mode. The MODE latch remains in its set status (Q=1). The SWITCHING PHASE: The Stand by signal is validated and the 200 A is sourced out of the Current Sense pin Transition from Stand by to Normal The secondary reconfiguration is removed. The regulation on the low voltage secondary rail can no longer be achieved, thus at the end of the SWITCHING PHASE, no PWM condition can be encountered. The LW latch is reset. At the next WORKING PHASE a NORMAL mode status takes place. In order to become independent of the recovery time SWITCHING PHASE constant on the secondary side of the SMPS an additional reset input R2 is provided on the MODE latch. The condition I demag <24 A corresponds to the activation of the secondary reconfiguration status. The R2 reset insures a return into the NORMAL mode following the first corresponds to 1V. START UP PHASE. Pulsed Mode Duty Cycle Control During the sleep mode of the SMPS the switch S3 is closed and the control input pin 3 is connected to

15 TCL OVERSEAS HOLDINGS LIMITED Service Manual 17 a 4.6V voltage source thru a 500 resistor. The discharge rate of the V CC capacitor is given by I CC latch (device consumption during the LATCHED OFF phase) in addition to the current drawn out of the pin 3. Connecting a resistor between the Pin 3 and GND (R DPULSED ) a programmable current is drawn from the V CC through pin 3. The duration of the LATCHED OFF phase is impacted by the presence of the resistor R DPULSED. The equation 3 shows the relation to the pin 3 current. Pulsed Mode Phases Equations 1 through 8 define and predict the effective behavior during the PULSED MODE operation. The equations 6, 7, and 8 contain K, Y, and D factors. These factors are combinations of measured parameters. They appear in the parameter section K factors for pulsed mode operation page 4. In equations 3 through 8 the pin 3 current is the current defined in the above section Pulsed Mode Duty Cycle Control. 2. TDA9801-Single standard VIF-PLL demodulator and FM-PLL detector FUNCTIONAL DESCRIPTION

16 18 Service Manual TCL OVERSEAS HOLDINGS LIMITED SYMBOL PIN DESCRIPTION VIF1 1 VIF differential input 1 VIF2 2 VIF differential input 2 TOP 3 tuner AGC TakeOver Point (TOP) connection ADJ 4 phase adjust connection MUTE 5 sound mute switch connection TPLL 6 PLL time constant connection CVBS 7 CVBS (positive) video output n.c. 8 not connected AF 9 AF output DAF 10 AF amplifier decoupling capacitor connection SI 11 sound intercarrier input TAGC 12 tuner AGC output VSO 13 video and sound intercarrier output VI 14 buffer amplifier video input AFC 15 AFC output VCO1 16 VCO1 reference circuit for 2fPC VCO2 17 VCO2 reference circuit for 2fPC GND 18 ground supply (0 V) AGC 19 AGC detector capacitor connection VP 20 supply voltage (+5 V) Stage IF amplifier The VIF amplifier consists of three AC-coupled differential amplifier stages. Each differential stage comprises a feedback network controlled by emitter degeneration. AGC detector, IF AGC and tuner AGC The automatic control voltage to maintain the video output signal at a constant level is generated in accordance with the transmission standard. Since the TDA9801 is suitable for negative modulation only the peak sync pulse level is detected. The AGC detector charges and discharges capacitor CAGC to set the IF amplifier and tuner gain. The voltage on capacitor CAGC is transferred to an internal IF control signal, and is fed to the tuner AGC to generate the tuner AGC output current on pin TAGC (open-collector output). The tuner AGC takeover point level is set at pin TOP. This allows the tuner to be matched to the SAW filter in order to achieve the optimum IF input level. Frequency detector and phase detector The VIF amplifier output signal is fed into a frequency detector and into a phase detector. During acquisition the frequency detector produces a DC current proportional to the frequency difference between the input and the VCO signal. After frequency lock-in the phase detector produces a DC current proportional to the phase difference between the VCO and the input signal. The DC current of

17 TCL OVERSEAS HOLDINGS LIMITED Service Manual 19 either frequency detector or phase detector is converted into a DC voltage via the loop filter which controls the VCO frequency. Video demodulator The true synchronous video demodulator is realized by a linear multiplier which is designed for low distortion and wide bandwidth. The vision IF input signal is multiplied with the in phase component of the VCO output. The demodulator output signal is fed via an integrated low-pass filter (f g = 12 MHz) for suppression of the carrier harmonics to the video amplifier. VCO, AFC detector and travelling wave divider The VCO operates with a symmetrically connected reference LC circuit, operating at the double vision carrier frequency. Frequency control is performed by an internal variable capacitor diode. The voltage to set the VCO frequency to the actual double vision carrier frequency is also amplified and converted for the AFC output current. The VCO signal is divided-by-2 with a Travelling Wave Divider (TWD) which generates two differential output signals with a 90 degree phase difference independent of the frequency. Video amplifier The composite video amplifier is a wide bandwidth operational amplifier with internal feedback. A nominal positive video signal of 1 V (p-p) is present at pin VSO. Buffer amplifier and noise clipper The input impedance of the 7 db wideband CVBS buffer amplifier (with internal feedback) is suitable for ceramic sound trap filters. Pin CVBS provides a positive video signal of 2 V (p-p). Noise clipping is provided internally. Sound demodulation LIMITER AMPLIFIER The FM sound intercarrier signal is fed to pin SI and through a limiter amplifier before it is demodulated. The result is high sensitivity and AM suppression. The limiter amplifier consists of 7 stages which areinternally AC-coupled in order to minimizing the DC offset. FM-PLL DETECTOR The FM-PLL demodulator consists of an RC oscillator, loop filter and phase detector. The oscillator frequency is locked on the FM intercarrier signal from the limiter amplifier. As a result of this locking, the RC oscillator is frequency modulated. The modulating voltage (AF signal) is used to control the oscillator frequency. By this, the FM-PLL operates as an FM demodulator. AF AMPLIFIER The audio frequency amplifier with internal feedback is designed for high gain and high common-mode rejection. The low-level AF signal output from the FM-PLL demodulator is amplified and buffered in a low-ohmic audio output stage. An external decoupling capacitor CDAF removes the

18 20 Service Manual TCL OVERSEAS HOLDINGS LIMITED DC voltage from the audio amplifier input. By using the sound mute switch (pin MUTE) the AF amplifier is set in the mute state. 3. TDA9874A Digital TV sound demodulator/decoder SYMBOL PIN DESCRIPTION EXTIR 1 external audio input right channel EXTIL 2 external audio input left channel Vref2 3 analog reference voltage for DAC and operational amplifiers P2 4 second general purpose I/O pin OUTM 5 analog output mono VSSA4 6 analog ground supply 4 for analog back-end circuitry OUTL 7 analog output left OUTR 8 analog output right VDDA1 9 analog supply voltage 1; back-end circuitry 5 V VSSA1 10 analog ground supply 1; back-end circuitry VSSD1 11 digital ground supply 1; core circuitry VDDD1 12 digital supply voltage 1; core voltage regulator circuitry VSSD2 13 digital ground supply 2; core circuitry TP2 14 additional test pin 2; connected to VSSD for normal operation NICAM 15 serial NICAM data output (at 728 khz) TP1 16 additional test pin 1; connected to VSSD for normal operation PCLK 17 NICAM clock output (at 728 khz) ADDR1 18 first I 2 C-bus slave address modifier input XTALO 19 crystal oscillator output XTALI 20 crystal oscillator input TEST2 21 test pin 2; connected to VSSD for normal operation Iref 22 resistor for reference current generation; front-end circuitry ADDR2 23 second I 2 C-bus slave address modifier input VSSA2 24 analog ground supply 2; analog front-end circuitry VDEC 25 analog front-end circuitry supply voltage decoupling TEST1 26 test pin 1; connected to VSSD for normal operation SIF2 27 sound IF input 2 Vref1 28 reference voltage; for analog front-end circuitry SIF1 29 sound IF input 1 CRESET 30 capacitor for Power-on reset VSSA3 31 digital ground supply 3; front-end circuitry VDDA3 32 analog front-end circuitry regulator supply voltage 3 (5 V) SCL 33 I 2 C-bus serial clock input SDA 34 I 2 C-bus serial data input/output SDO 35 I 2 S-bus serial data output WS 36 I 2 S-bus word select input/output SCK 37 I2S-bus clock input/output

19 TCL OVERSEAS HOLDINGS LIMITED Service Manual 21 SYSCLK 38 system clock output VDDD3 39 digital supply voltage 3; digital I/O pads VSSD3 40 digital ground supply 3; digital I/O pads P1 41 first general purpose I/O pin MONOIN 42 analog mono input FUNCTIONAL DESCRIPTION Description of the demodulator and decoder section 1. SIF INPUTS Two inputs are provided, pin SIF1 and pin SIF2. For higher SIF signal levels the SIF input can be attenuated with an internal switchable 10 db resistor divider. As no specific filters are integrated, both inputs have the same specification giving flexibility in application. The selected signal is passed through an AGC circuit and then digitized by an 8-bit ADC operating at MHz. 2. AGC The gain of the AGC amplifier is controlled from the ADC output by means of a digital control loop employing hysteresis. The AGC has a fast attack behaviour to prevent ADC overloads, and a slow decay behaviour to prevent AGC oscillations. For AM demodulation the AGC must be switched off. When switched off, the control loop is reset and fixed gain settings can be chosen. The AGC can be controlled via the I2C-bus. 3. MIXER The digitized input signal is fed to the mixers, which mix one or both input sound carriers down to zero IF. A 24-bit control word for each carrier sets the required frequency. Access to the mixer control word registers is via the I 2 C-bus or via Easy Standard Programming (ESP). When receiving NICAM programs, a feedback signal is added to the control word of the second carrier mixer to establish a carrier-frequency loop. 4. FM AND AM DEMODULATION An FM or AM input signal is fed through a switchable band-limiting filter into a demodulator that can be used for either FM or AM demodulation. Apart from the standard (fixed) de-emphasis characteristic, an adaptive de-emphasis is available for Wegener-Panda 1 encoded satellite programs. 5. FM DECODING A 2-carrier stereo decoder recovers the left and right signal channels from the demodulated sound carriers. Both the European and Korean stereo systems are supported. Automatic FM dematrixing is also supported, which means that the FM sound mode identification

20 22 Service Manual TCL OVERSEAS HOLDINGS LIMITED (mono, stereo or dual) switches the FM dematrix directly. No loop via the microcontroller is needed. For highly overmodulated signals, a high deviation mode for monaural audio sound single carrier demodulation can be selected. NICAM decoding is still possible in high deviation mode. 6. FM IDENTIFICATION The identification of the FM sound mode is performed by AM synchronous demodulation of the pilot and narrow-band detection of the identification frequencies. The result is available via the I2C-bus interface. A selection can be made via the I2C-bus for B/G, D/K and M standards, and for three different time constants that represent different trade-offs between speed and reliability of identification. A pilot detector allows the control software to identify an analog 2-carrier (A2) transmission within approximately 0.1 s.

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